Epoxy resins, which are excellent in cost performance, are widely used as insulating materials for printed wiring boards. In recent years, these epoxy resins have also been required to have higher-functional physical properties to, for example, support a higher density of wiring. By way of example, for printed wiring boards used in high frequency applications such as satellite communications, there has been a need for an insulating material having excellent dielectric characteristics such as a low dielectric constant and a low loss tangent in view of preventing signal delay.
The use of a polyphenylene ether as one of the materials excellent in dielectric characteristics has been known since the 1970s or so. However, a high-molecular polyphenylene ether is very poor in moldability because of its high melt viscosity. For example, Patent Documents 1 and 2 also each describe a process for producing a laminated board by preparing a toluene solution of a polyphenylene ether and impregnating the toluene solution into a substrate while heating the solution. However, such a process is very dangerous which involves impregnating a toluene solution while heating the solution.
In addition, a polyphenylene ether is generally poor in compatibility with an epoxy resin. Thus, when a simple mixture of the polyphenylene ether with the resin is used as a raw material for a molded article, it often represents a challenge to improve the mechanical strength of the resulting molded article.
To solve these problems, Patent Documents 3 and 4 each describe a process for producing a modified polyphenylene ether by converting a polyphenylene ether into a lower-molecular polymer by a redistribution reaction and epoxidizing the polymer using epichlorohydrin.
Patent Documents 5 and 6 each also describe a process which involves producing a low-molecular form of polyphenylene ether by a polymerization method and then epoxy-modifying the polyphenylene ether.    [Patent Document 1] Japanese Patent No. 2667625    [Patent Document 2] Japanese Patent No. 3300426    [Patent Document 3] JP-A-9-235349    [Patent Document 4] Japanese Patent No. 3248424    [Patent Document 5] WO2004/104097    [Patent Document 6] JP-A-2004-256717